Method for reception of long range signals in bluetooth

ABSTRACT

The invention of a method for reception of long transmission range Bluetooth signals impaired by multipath are disclosed. The new reception method proposed allows to increase the transmission range for data transmission in Bluetooth. The invention proposes the use of a new FDE adapted to SC transmission without a GI or CP. The proposed FDE very successfully mitigates ISI while being very implemention-friendly.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of co-pending application Ser. No.11/435,948, filed on May 18, 2006, and for which priority is claimedunder 35 U.S.C. 120, the entire contents of all of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for reception of Bluetoothsignals, and more especially, to a method for reception of long-rangesignals in Bluetooth.

2. Background of the Related Art

The Bluetooth standard distinguishes devices by their so-called powerclass {[IEEE 802.15.1], [BT SIG 1.2], [BT SIG EDR]}. For each powerclass, a maximum output power (Pmax), a nominal output power and aminimum output power is specified as shown in Table 1.

TABLE 1 Maximum Nominal Minimum Power Output Output Output Class Power(Pmax) Power Power Power Control 1 100 mW N/A   1 mW (0 dB) Pmin <+4 dBm(20 dBm) to Pmax Optional: Pmin² to Pmax 2 2.5 mW 1 mW 0.25 mW (−6Optional: (4 dBm) (0 dBm) dBm) Pmin² to Pmax 3 1 mW N/A N/A Optional: (0dBm) Pmin² to Pmax

The Bluetooth technology is intended to implement wireless personal areanetworks (WPAN). Therefore, the typical range of Bluetooth devices isexpected to be limited to about 10 meters. Bluetooth devices accordingto power class 1, however, are capable to transmit over a rangesignificantly larger than the so-called personal operating space (POS)of about 10 meters.

[IEEE 802.15.1]: the IEEE Std 802.15.1-IEEE Standard for Informationtechnology Telecommunications and information exchange between systemsLocal and metropolitan area networks Specific requirements-Part 15.1:Wireless Medium Access Control (MAC) and Physical Layer (PHY)Specifications for Wireless Personal Area Networks (WPANs), 14 Jun.2002.

[BT SIG 1.2]: Bluetooth SIG Specification of the Bluetooth System,Version 1.2, 5 Nov. 2003.

[BT SIG EDR]: Bluetooth SIG Specification of the Bluetooth System withEDR, Version 2.0, 4 Nov. 2004.

Sensitivity Performance in Bluetooth

In [BT SIG EDR], a reference sensitivity level of −70 dBm is given foran uncoded bit error rate (BER) of 0.0001 (0.01%). In FIG. 1 and FIG. 2,the uncoded BER versus SNR is shown for PI/4-DQPSK and D8PSK,respectively. For PI/4-DQPSK, about 14 dB SNR are needed to achieve anuncoded BER of 0.01%. For D8PSK, about 20 dB SNR are needed to achievean uncoded BER of 0.01%. Additional SNR margin is needed to accommodatefixed-point implementation losses as well as losses introduced by radiofront end impairments and non-ideal time and frequency synchronization.Therefore, about 25 dB SNR are assumed to achieve an uncoded BER of0.01%.

Path Loss in Bluetooth

The signal power received by a Bluetooth device depending on the signalpower transmitted by another Bluetooth device is given by Equation 1:

P _(RX) =P _(TX) −L _(Path) −L _(Fade) +G _(TX) +G _(RX)  (1)

with

-   -   P_(RX): received signal power    -   P_(TX): transmitted signal power    -   L_(Path): path loss    -   L_(Fade): fade margin    -   G_(TX): received antenna gain    -   G_(RX): transmit antenna gain        The following assumptions are applied in Equation 2 and Equation        3:

G_(TX)=G_(RX)=0 dBi  (2)

L_(Fade)=8 dB  (3)

Therefore, based on Equation 1 and Equation 2, the path loss is given byEquation 4:

L _(Path) =P _(TX) −P _(RX)−8 dB  (4)

The transmitted signal power under consideration (maximum signal power)is in Equation 5:

P _(TX)

P _(TX,max)=20 dBm (Power class 1 device)  (5)

The received signal power under consideration (minimum signal power) isgiven by Equation 6:

P _(RX)

P _(RX,min) =N _(Floor) +W+SNR _(RX) +NF _(RX)  (6)

with

-   -   P_(Tx,max): maximum transmit power    -   P_(RX,min): minimum received power    -   N_(Floor): noise floor due to thermal noise    -   W: noise bandwidth    -   SNR_(RX): signal-to-noise-ratio required for BER=0.0001 for        D8PSK    -   NF_(Rx): receiver noise figure

The noise floor due to thermal noise amounts to −174 dBm per Hz signalbandwidth. The signal bandwidth for Bluetooth technology equals 1 MHz.The receiver noise figure is assumed to be 20 dB.

The minimum signal power can now be computed by Equation 7:

$\begin{matrix}\begin{matrix}{P_{{RX},\min} = {{{- 174}\mspace{14mu} {dBm}\text{/}{Hz}} + {1\mspace{14mu} {MHz}} + {25\mspace{14mu} {dB}} + {20\mspace{14mu} {dB}}}} \\{= {{{- 114}\mspace{14mu} {dBm}} + {45\mspace{14mu} {dB}}}} \\{= {{- 69}\mspace{14mu} {dBm}}}\end{matrix} & (7)\end{matrix}$

The maximum path loss based on maximum transmit signal power and minimumreceived signal power and fade margin based on Equation 4 is now givenby Equation 8:

$\begin{matrix}\begin{matrix}{L_{{Path},\max} = {P_{{TX},\max} - P_{{RX},\min} - {8\mspace{14mu} {dB}}}} \\{= {{20\mspace{14mu} {dB}} + {69\mspace{14mu} {dB}} - {8\mspace{14mu} {dB}}}} \\{= {81\mspace{14mu} {dB}}}\end{matrix} & (8)\end{matrix}$

It follows that the maximum path loss for a Bluetooth device of powerclass 1 equals 81 dB. For power class 2 and power class 3, the maximumpath loss amounts to 73 dB and 69 dB, respectively.

On Transmission Range in Bluetooth

The path loss depending on the transmission range for line-of-sight(LOS) conditions in a Bluetooth network is given by Equation 9:

$\begin{matrix}{L_{Path} = {20\; {\log \left( {\frac{4\Pi}{\lambda}R} \right)}}} & (9)\end{matrix}$

or by Equation 10 approximately

L _(Path)=40+20 log(R)  (10)

with

-   -   R: transmission range in [meters]    -   λ: wavelength of transmission signal

The path loss depending on the transmission range for non-line-of-sight(NLOS) conditions in a Bluetooth network is given by Equation 11.

$\begin{matrix}{L_{Path} = {{36\; {\log \left( {\frac{4\Pi}{\lambda}R} \right)}} - {46.7\mspace{14mu} {dB}}}} & (11)\end{matrix}$

or Equation 12 approximately

L _(Path)=25.3+36 log(R)  (12)

Equation 9, by Equation 10, Equation 11 and Equation 12 are visualizedin FIG. 3. It follows that for a maximum pathloss of 81 dB, a maximumtransmission range R_(max) of 113 meters (in large office) is achieved(LOS conditions) using a power class 1 device while ensuring reliablecommunication. For power class 2 and power class 3, 18 meters (in smalloffice) and 11 meters (POS) are achieved, respectively.

On Multipath Propagation in Bluetooth

In Bluetooth, the symbol rate equals 1 Msps while the symbol durationT_(symbol) equals 1 μs (1000 ns). According the radio propagationtheory, a radio frequency signal propagates 300 m in 1 μs (3e8 metersper second). The maximum echo delay (1st versus 2nd echo) based on themaximum transmission range is given by Equation 13:

$\begin{matrix}\begin{matrix}{D_{\max} = {\frac{T_{Symbol}}{300\mspace{14mu} m} \cdot R_{\max}}} \\{= {\frac{1\mspace{14mu} {µs}}{300\mspace{14mu} m}113\mspace{14mu} m}} \\{= {377\mspace{14mu} {ns}}}\end{matrix} & (13)\end{matrix}$

It follows that for a maximum transmission range R_(max) of 113 meters amaximum echo delay of 377 ns is obtained.

For power class 2 and power class 3, 60 ns and 37 ns are obtained,respectively.

Multipath propagation results in inter-symbol interference (ISI). Theamount of ISI introduced depends on the number and power of all echopaths following the first arriving path.

Using the result from Equation 13, one gets a maximum ISI percentageshown in Equation 14:

$\begin{matrix}\begin{matrix}{{ISI}_{\max} = \frac{D_{\max}}{T_{Symbol}}} \\{= \frac{377\mspace{14mu} {ns}}{1\mspace{14mu} {µs}}} \\{= {37.7\%}}\end{matrix} & (14)\end{matrix}$

For power class 2 and power class 3, 6% and 3.7% are obtained,respectively.

The ISI is modelled as an echo path having a relative power (withregards to the first arriving path) equal to ISI_(max). With thatassumption, a worst-case multipath channel profile with a 1st(obstructed) path @ 0 dB w/ delay of 0 samples and a 2nd path (echo)@10*log₁₀(0.377)=−4.24 dB w/ delay of 1 sample (1 μs).

The 2-path multipath propagation model for Bluetooth long transmissionrange applications is shown in FIG. 4. A large office scenario forBluetooth long transmission range applications is shown in FIG. 5.

Impact of Multipath Propagation on Bluetooth Demodulation Performance

In FIG. 6, FIG. 7, FIG. 8, and FIG. 9, the simulated impact of multipathpropagation on Bluetooth EDR demodulation performance is shown.

For the 2-path multipath propagation model, the power of the second pathis varied relative to the first arriving path. For the exponentialmultipath propagation model, the RMS delay spread is varied.

In FIG. 6, one can see that even for Pi/4-DQPSK and a very small secondpath such as −15 dB (10 log₁₀(0.0313)), there is a degradation exceeding3 dB already. For path larger than −9 dB (10 log₁₀(0.125)), successfuldemodulation is no longer possible independent of the SNR.

In FIG. 7, one can see that even for D8PSK and a very small second pathsuch as −15 dB (10 log₁₀(0.0313)), there is a degradation exceeding 12dB (!) already. For path larger than −15 dB, successful demodulation isno longer possible independent of the SNR.

In FIG. 8, one can see that for Pi/4-DQPSK and an RMS delay spread >250ns, there is a degradation exceeding 3 dB.

In FIG. 9, one can see that for D8PSK and an RMS delay spread >200 ns,there is a degradation exceeding 3 dB.

It was also shown that even for very moderate multipath propagation, noreliable data transmission using Bluetooth technology is possible. Thatis due to the inter-symbol interference (ISI) introduced by multipathpropagation. Current (state-of-the-art) Bluetooth receivers are notcapable of mitigating the unfavorable impact of ISI on the datademodulation in Bluetooth.

It is concluded that with current (state-of-the-art) Bluetoothreceivers, no reliable data transmission is possible with regards totransmission ranges provided the transmission power of power class 1devices.

SUMMARY OF THE INVENTION

In order to solve the problems mentioned above, the present inventionprovides a method for reception of long-range signals in Bluetooth. Thepresent invention processes Bluetooth signals with linear minimum meansquare error (MMSE) frequency-domain equalization (FDE) in singlecarrier (SC) system using a Fourier Transform and provides longtransmission range Bluetooth service with reliable data transmission.

The present invention improves the performance of Bluetooth servicebased on power class 2 and 3 devices in multipath environment.

The present invention provides FFT/IFFT-based MMSE SC FDE receiving modefor all Bluetooth transmission modes for low-complexity andhigh-performance

The present invention is used in multi-standard devices in efficientimplementation by reuse of the FFT/IFFT circuitry

To achieve the purpose mentioned above, one embodiment of the presentinvention provides a method for reception of long-range signals inBluetooth is for all transmission modes on power class 1, power class 2and power class 3, the method comprising: receiving Bluetooth signals;and processing signals with linear frequency-domain equalization (FDE)in single carrier (SC) system using a Fourier Transform.

BRIEF DESCRIPTION OF THE DRAWINGS

The file of this patent contains at least one drawing executed in color.Copies of this patent with color drawing(s) will be provided by thePatent and Trademark Office upon request.

The foregoing aspects and many of the accompanying advantages of thisinvention will becomes more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 illustrating BER versus SNR for PI/4-DQPSK in AWGN;

FIG. 2 illustrating BER versus SNR for D8PSK in AWGN;

FIG. 3 illustrating the pathloss versus transmission range in aBluetooth network;

FIG. 4 illustrating 2-path multipath propagation model for Bluetoothlong transmission range applications;

FIG. 5 illustrating the scenario of multipath propagation in largeoffice;

FIG. 6 illustrating the BER performance for Pi/4-DQPSK in 2-Pathmultipath;

FIG. 7 illustrating the BER performance for D8PSK in 2-path multipath;

FIG. 8 illustrating the BER performance for Pi/4-DQPSK in exponentialmultipath;

FIG. 9 illustrating the BER performance for D8PSK in exponentialmultipath;

FIG. 10 illustrating the processing flow of h yielding H_(inv) in SClinear MMSE BLE according to one embodiment of the present invention;

FIG. 11 illustrating h of exponential channel (left) and correspondingh_(inv) using M=64 (right);

FIG. 12 illustrating the Pole-Zero Diagrams of h of exponential channel(left) and corresponding h_(inv) using M=64 (right);

FIG. 13 illustrating the constellation diagrams for noiseless QPSKbefore equalization (left) and after equalization (right);

FIG. 14 illustrating the constellation diagrams for noiseless QPSKbefore equalization (left) and after equalization (right);

FIG. 15 illustrating the performance of Pi/4-DQPSK and FDE in 2-pathmultipath (varying N);

FIG. 16 illustrating the performance of D8PSK and FDE in 2-pathmultipath (N=64);

FIG. 17 illustrating the performance of D8PSK and FDE in 2-pathmultipath (varying N);

FIGS. 18A, 18B and 18C illustrating the functional block diagram ofBluetooth transmitter;

FIG. 19 illustrating the functional block diagram of radio channel modelfor Bluetooth transmission: introduction of multipath fading andadditive White Gaussian Noise (AWGN); and

FIGS. 20A and 20B illustrating the functional Block Diagram of BluetoothReceiver according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As an invention, the use of equalization is proposed for Bluetooth datacommunication.

While ISI mitigation by equalization is well-known in state-of-the-artdigital wireless communications engineering, this invention proposes theuse of a new FDE adapted to SC transmission without a GI or CP. Theproposed FDE very successfully mitigates ISI while being veryimplemention-friendly.

The resulting performance of long transmission range Bluetooth servicebased on power class 1 devices using BlueWARP technology is beyondstate-of-the-art Bluetooth service based on power class 1 devices.

In the following, a generalized system model is introduced. The model issimilar to the one proposed in [Klein].

At the transmit side, a block (vector) d of data of length N is formedin Equation 15:

d=(d ₁ ,d ₂ . . . d _(N))^(T)  (15)

Any coding, modulation or spreading is assumed to be included in dalready. The data block is transmit through a channel characterized byits impulse response h in Equation 16:

h=(h ₁ ,h ₂ . . . h _(w))^(T)  (16)

The convolution of d and h is expressed in matrix notation using thematrix H in Equation 17:

H=(H _(i,v)), i=1 . . . N+W−1, v=1 . . . N  (17)

with Equation 18:

$\begin{matrix}{H_{i,v} = \left\{ \begin{matrix}h_{i - v + 1} & {1 \leq {i - v + 1} \leq W} \\0 & {else}\end{matrix} \right.} & (18)\end{matrix}$

The received signal r is given by Equation 19:

$\begin{matrix}\begin{matrix}{r = \left( {r_{1},{r_{2}\mspace{14mu} \ldots \mspace{14mu} r_{N + W - 1}}} \right)^{T}} \\{= {{H \cdot d} + n}}\end{matrix} & (19)\end{matrix}$

where n denotes an additive white Gaussian noise sequence with zero meanand covariance matrix R_(nn).

Using (block) linear equalization technique for SC systems, an estimateof the transmit data is obtained using one of the following criteria.Equation 20: Matched Filter (MF) Criterion

{circumflex over (d)} _(MF) =H ^(H) ·r  (20)

Equation 21: Zeros Forcing (ZF) Criterion

{circumflex over (d)} _(ZF)=(H ^(H) ·H)⁻¹ ·H ^(H) ·r  (21)

Equation 22: Minimum Mean Square Error (MMSE) Criterion

{circumflex over (d)} _(MMSE)=(H ^(H) ·H+σ ²)⁻¹ ·H ^(H) ·r  (22)

Typically, the MMSE criterion yields superior results. Therefore, onlythe MMSE criterion is pursued. Nevertheless, all newly proposed receiverarchitectures are applicable as well to MF or ZF equalization.

Single Carrier Linear MMSE Frequency-Domain Equalization using FFTwithout Guard Period

In order to avoid complex receiver processing tasks such as Choleskydecomposition for solving Equation 22, the (block) linear MMSEequalization for SC systems can be performed efficiently in frequencydomain expressed in Equation 23 and Equation 24:

$\begin{matrix}{{\hat{d}}_{MMSE} = {F^{- 1}\left\{ {H_{inv} \cdot {F(r)}} \right\}}} & (23) \\{H_{inv} = \frac{\left( {F\left\{ \hat{h} \right\}} \right)^{*}}{{{\left( {F\left\{ \hat{h} \right\}} \right)^{*} \cdot F}\left\{ \hat{h} \right\}} + \sigma^{2}}} & (24)\end{matrix}$

where F denotes the Discrete Fourier Transform (DFT), F⁻¹ denotes theInverse Discrete Fourier Transform (IDFT).ĥ refers to an estimated channel impulse response. The ĥ is obtained bya separate processing step typically called channel estimation.H_(inv) represents the frequency response of the propagation channelbeing inverted using the MMSE criterion. Its time-domain equivalent isgiven by h_(inv).

For actual implementations, DFT and IDFT are realized by Fast FourierTransform (FFT) and Inverse Fast Fourier Transform (IFFT), respectively.

H_(inv) in Equation 23 can be interpreted as the frequency response of atransversal linear equalizer filter which time (impulse) response has tobe convolved with the received signal r. The filter can be categorizedas an IIR filter. Therefore, the filter length is infinite. However, alength can be defined which contains most of the large coefficients andneglects small coefficients. The length of this approximated equalizerfilter is denoted by L_(eq).

The length of the received data blocks varies significantly depending onpacket type and service. A fixed-length FFT/IFFT implementation based onthe maximum data block length N of all packet types and services to beintegrated in the receiver architecture would not be efficient. Also, Ncan be rather large (>2̂13) which would require to implement a very largeFFT (>8 k). However, it is well-known that convolution (e.g. filtering)operations for continuous data streams or long blocks of data can beimplemented efficiently using overlap-add-technique (OAT) FFT oroverlap-save-technique (OST) FFT algorithms. The further descriptionfocuses on OAT FFT.

As suggested in [Falconer], FDE for SC systems requires a GI to beinserted at the transmitter. The following method, however, allows toapply FFT-based FDE as well for systems without GI.

An M-point FFT (M=8, 16, 32, 64) is assumed. For every M-point FFT/IFFTbased convolution operation, a length M-L_(eq) output data block isgenerated. The start index within the data block is advanced by M-L_(eq)samples per FFT-IFFT operation.

The single FFTs/IFFTs overlap by L_(eq) samples. Therefore, L_(eq)<M/2must hold. For such short FFT/IFFT sizes, the approximated equalizerfilter must be limited which can be accomplished either by circularconvolution with a rectangular window transformed into frequency domainRW (see equation 26) or by multiplication with a rectangular window rwin time domain (see equation 25). The latter approach requires oneadditional frequency-time and time-frequency conversion.

The extended versions of Equation 23 are given below:

$\begin{matrix}{{\hat{d}}_{MMSE} = {F^{- 1}\left\{ {F{\left\{ {F^{- 1}{\left\{ \frac{\left( {F\left\{ \hat{h} \right\}} \right)^{*}}{{{\left( {F\left\{ \hat{h} \right\}} \right)^{*} \cdot F}\left\{ \hat{h} \right\}} + \sigma^{2}} \right\} \cdot {rw}}} \right\} \cdot {F(r)}}} \right\}}} & (25) \\{{\hat{d}}_{MMSE} = {F^{- 1}\left\{ {\left( {\frac{\left( {F\left\{ \hat{h} \right\}} \right)^{*}}{{{\left( {F\left\{ \hat{h} \right\}} \right)^{*} \cdot F}\left\{ \hat{h} \right\}} + \sigma^{2}} \otimes {RW}} \right) \cdot {F(r)}} \right\}}} & (26)\end{matrix}$

denotes circular convolution.

Also, h_(inv) must be shifted into the correct position. Performing thisoperation in frequency domain corresponds to rotating H_(inv) withphasors having an angle increasing with every sample of H_(inv)

In FIG. 10, the entire processing flow of ĥ yielding H_(inv) isdepicted:

S01: FFT on estimated channel impulse response

S02: conjugate complex operation on Ĥ

S03: Multiplication of Ĥ with conj(Ĥ)

SO4: Addition of Ĥ·H* with σ²

S05: Division of Ĥ* by Ĥ·H*+σ²

S06: Multiplication with phasors

$1 \cdot ^{j\frac{k}{M}}$

S07: Circular convolution with

$\frac{\sin \; x}{x}$

SC Linear MMSE FDE

In FIG. 11, h of a noiseless exponential multipath channel withoutfading (upper subplot) and with fading (lower subplot) is shown. Thechannel parameter RMS delay spread s was set to s=150 ns. In addition,one can see the corresponding h_(inv) which was obtained by convertingH_(inv) from Equation 24 back to time domain.

In order to apply OAT for equalization, h_(inv) has to be shortened tothe overlap length M/2. This shortened h_(inv) is constructed using thelast quarter of samples of h_(inv) and appending the first quarter ofsamples of h_(inv) to it.

In FIG. 12, one can see the impact of the minimum-phase/non-minimumphase character of the non-fading/fading exponential channel on thepole-zero diagrams of h and h_(inv).

FIG. 13, visualizes the successful outcome of the described equalizationprocess by comparing noiseless QPSK constellations before and after SClinear MMSE FDE. In non-faded multipath conditions, the equalizedconstellation appears again to be perfect. In multipath fadingconditions, however, some noise-like interference remains.

Bluetooth Demodulation Performance in Multipath Propagation using SCLinear MMSE FDE

In FIG. 14, FIG. 15, FIG. 16 and FIG. 17, the Bluetooth EDR demodulationperformance using SC linear MMSE FDE is demonstrated. In addition, thesimulated impact of multipath propagation on Bluetooth EDR demodulationperformance is shown.

For the 2-path multipath propagation model, the power of the second pathis varied relative to the first arriving path.

In FIG. 14, one can see that for Pi/4-DQPSK and severe multipathconditions (second path as high as −3 dB (10 log₁₀(0.5)), thedegradation in demodulation performance is limited to 3 dB. The FFT sizeMapplied equals 64.

In FIG. 15, one can see that for Pi/4-DQPSK and a strong second path (−6dB), M=128 and M=32 perform as well as M=64. Even M=16 performs within 1dB of the optimum performance (M=128). Very small FFT sizes (M<16) causeservere degradation in equalization (and therefore demodulation)performance.

In FIG. 16, one can see that for D8PSK and severe multipath conditions(second path as high as −3 dB (10 log₁₀(0.5)), the degradation indemodulation performance is limited to 3 dB. The FFT size Mappliedequals 64.

In FIG. 17, one can see that for D8PSK and a strong second path (−6 dB),M=128 and M=32 perform as well as M=64. Even M=16 performs within 2 dBof the optimum performance (M=128). Very small FFT sizes (M<16) causesevere degradation in equalization (and therefore demodulation)performance.

It was shown that for Bluetooth SC linear MMSE FDE can be used toefficiently mitigate severe ISI introduced by multipath propagation(second path as high as −3 dB (10 log₁₀(0.5)). In addition, it wasdemonstrated that using FFT sizes as small as M=16 still allow forequalization (and therefore demodulation) performance within 2 dB of theoptimum performance using M=128.

Integration with a Bluetooth Receiver

In this section, it is described how to integrate the SC linear MMSE FDEinto a Bluetooth receiver. The integration is described on a conceptualsystem level.

The SC linear MMSE FDE is assumed to be used for EDR only. However, itcan also be used for Basic Rate without modifications.

In FIG. 18A, FIG. 18B and FIG. 18C, a (simplified) functional blockdiagram of a Bluetooth transmitter according to [BT SIG EDR] is shown:

-   -   FIG. 18A        -   The packet header and the packet data (payload) undergo            bitstream processing as described in Volume 2 Core System            Package, Part B Baseband Specification, Chapter 7: Bitstream            Processing (encryption is not shown).        -   Bitstream-processed packet header and access code are            multiplexed as described in Volume 2 Core System Package,            Part B Baseband Specification, Chapter 6: Packets.        -   Bitstream-processed and multiplexed packet header and access            code are GFSK modulated as described in Volume 2 Core System            Package, Part A Radio Specification, Chapter 3: Transmitter            Characteristics.    -   FIG. 18B        -   Bitstream-processed packet data (payload) is switched            between either Basic Rate or EDR processing:            -   Basic Rate: Bitstream-processed packet data (payload) is                GFSK modulated            -   EDR: Sync sequence and trailer are multiplexed with                bitstream-processed packet data (payload)            -   EDR: Multiplexed sync                sequence/trailer//bitstream-processed packet data                (payload) is switched between Pi/4-DQPSK modulation or                D8PSK modulation            -   EDR: Multiplexed and modulated sync                sequence/trailer//bitstream-processed packet data                (payload) is multiplexed with guard            -   EDR: guard and multiplexed and modulated sync                sequence/trailer//bitstream-processed packet data                (payload) is filtered upsampled (US) with                root-raised-cosine (RRC) filter as described in Volume 2                Core System Package, Part A Radio Specification, Chapter                3: Transmitter Characteristics    -   FIG. 18C        -   Processed access code, packet header and packet data            (payload) is multiplexed forming a complete transmit packet

In FIG. 19, a functional block diagram of the radio channel model usedfor Bluetooth transmission is depicted. It introduces multipath fadingaccording to the model described in prior art. Also, it introducesAdditive White Gaussian Noise (AWGN).

In FIG. 20A and FIG. 20B, a (simplified) functional block diagram of aBluetooth receiver is shown:

-   -   FIG. 20A        -   A de-multiplxer 101 demultiplexing packet header and packet            data (payload) (access code-related processing is not shown)        -   Packet data (payload) is switched by a switch 102 between            either Basic Rate or EDR processing:            -   Basic Rate: packet data (payload) is processed by a                FFT-based equalizer 105, and then demodulated by a GFSK                demodulator 108.            -   Basic Rate: optional equalization of packet header using                SC linear MMSE FDE (estimation of channel impulse                response not shown).            -   Basic Rate: GFSK demodulation of packet header by a GFSK                demodulator 107.            -   EDR: Packet data (payload) is filtered downsampled (DS)                with root-raised-cosine (RRC) filter 103 (guard, sync                sequence and trailer processing is not shown).            -   EDR: filtered packet data (payload) is switched by a                switch 104 between Pi/4-DQPSK demodulation or D8PSK                demodulation.            -   EDR: equalization of packet data (payload) using SC                linear MMSE FDE (estimation of channel impulse response                not shown)            -   EDR: Pi/4-DQPSK demodulation or 8-DPSK demodulation of                packet data (payload) by a Pi/4-DQPSK demodulator 109 or                an 8-DPSK demodulator 110.    -   FIG. 20B        -   EDR: reverse bitstream-processing on packet data (payload)

The key in the description of the (simplified) processing flow in aBluetooth receiver applying BlueWARP technology is the positioning of SClinear MMSE FDE directly before Pi/4-DQPSK demodulation or D8PSKdemodulation.

Accordingly, one of features of the present invention is to provide amethod for reception of long-range signals in Bluetooth. The method hasoutstanding performance of long transmission range Bluetooth servicebased on power class 1 devices and performance improvement of Bluetoothservice based on power class 2 and 3 devices in multipath environment.

Accordingly, the Low-complexity/high-performance FFT/IFFT-based MMSE SCFDE receiver architecture is used for all Bluetooth transmission modesand has highly efficient implementation by reuse of the FFT/IFFTcircuitry in the context of multi-standard devices,

Although the present invention has been explained in relation to itspreferred embodiment, it is to be understood that other modificationsand variation can be made without departing the spirit and scope of theinvention as hereafter claimed.

1. A method for reception of long-range signals in Bluetooth for alltransmission modes on power class 1, power class 2 and power class 3,the method comprising: receiving Bluetooth signals; and processing saidBluetooth signals with linear frequency-domain equalization (FDE) insingle carrier (SC) system using a Fourier Transform.
 2. The method forreception of long-range signals in Bluetooth according to claim 1,wherein said Fourier Transform is a Discrete Fourier Transform (DFT)deduced from a Fast Fourier Transform (FFT).
 3. The method for receptionof long-range signals in Bluetooth according to claim 2, wherein saidFast Fourier Transform (FFT) is overlap-add-technique FFT oroverlap-save-technique FFT.
 4. The method for reception of long-rangesignals in Bluetooth according to claim 1, wherein said FourierTransform is an Inverse Discrete Fourier Transform deduced from anInverse Fast Fourier Transform (IFFT).
 5. The method for reception oflong-range signals in Bluetooth according to claim 4, wherein saidInverse Fast Fourier Transform (IFFT) is overlap-add-technique IFFT oroverlap-save-technique IFFT.
 6. The method for reception of long-rangesignals in Bluetooth according to claim 1, further comprising executingan estimate of the transmit data after receiving said Bluetooth signals.7. The method for reception of long-range signals in Bluetooth accordingto claim 6, wherein said estimate of the transmit data is obtained usingMatched Filter (MF) criterion.
 8. The method for reception of long-rangesignals in Bluetooth according to claim 6, wherein said estimate of thetransmit data is obtained using Zero Forcing (ZF) criterion.
 9. Themethod for reception of long-range signals in Bluetooth according toclaim 6, wherein said estimate of the transmit data is obtained usingMinimum Mean Square Error (MMSE) criterion.
 10. The method for receptionof long-range signals in Bluetooth according to claim 9, wherein saidminimum mean square error (MMSE) is obtained from{circumflex over (d)} _(MMSE) =F ⁻¹ {H _(inv) ·F(r)} and H_(inv) isobtained from$H_{inv} = \frac{\left( {F\left\{ \hat{h} \right\}} \right)^{*}}{{{\left( {F\left\{ \hat{h} \right\}} \right)^{*} \cdot F}\left\{ \hat{h} \right\}} + \sigma^{2}}$11. The method for reception of long-range signals in Bluetoothaccording to claim 10, wherein said F and F⁻¹ size is 8 or
 16. 12. Themethod for reception of long-range signals in Bluetooth according toclaim 9, wherein said minimum mean square error (MMSE) comprises: usingFFT on estimated channel impulse response ĥ yielding Ĥ; conjugatingcomplex operation on Ĥ; multiplying of Ĥ with conj(Ĥ); adding of Ĥ·H*with σ²; dividing of Ĥ* by Ĥ·H*+σ²; multiplying with phasors${1 \cdot ^{j\frac{k}{M}}};$ and circulating circular convolution with$\frac{\sin \; x}{x}.$
 13. The method for reception of long-rangesignals in Bluetooth according to claim 1, wherein said transmissionmodes comprises 1 Mbps transmission mode (GFSK), 2 Mbps transmissionmode (DPSK), and 3 Mbps transmission mode (DPSK).